Jeffrey Petruska, Ph.D.
Jeffrey Petruska, Ph.D.
Department of Anatomical Sciences & Neurobiology
Department of Neurological Surgery
Laboratory of Neural Physiology and Plasticity
In terms of biological principles, we investigate the cellular and molecular mechanisms regulating anatomical and electrophysiological plasticity of neurons, focusing on the peripheral nervous system and spinal cord. We are particularly interested in the interaction between, and co-regulation of, the anatomical and electrophysiological properties of neurons. We study these principles in the context of spinal cord injury and the spinal pain system (particularly in the context of damage to peripheral tissue which is a common and chronic issue for the SCI population and is an etiological factor in the development of chronic pain).
In terms of biomedical questions, we investigate:
1) Effects of spinal cord injury and post-SCI treatments on the function of motor and sensory neurons
2) Mechanisms and consequences of sensory neuron responses to tissue damage3) Mechanisms and consequences of adult axonal collateral sprouting
These hypothesis-driven projects are well-coordinated when viewed in the context of my long-term vision – understanding how sensory input to the spinal cord below an injury influences the function of the remaining circuitry. It is my proposition that the combined effects of spinal cord injury and inflammatory secondary conditions act in concert to induce “circuit dysfunction” in the spinal cord caudal to an injury due to an unchecked, overactive, and highly plastic spinal nociceptive system. Unfortunately, SCI-related secondary conditions are rarely considered in basic neuroscience research, in spite of their high degree of clinical relevance and importance to the SCI community. On the other hand, the status of spinal circuits below an injury is a topic of a great deal of basic science study, but principally in the context of acute lacerations intended to determine the role of specific tracts, and much less-so in the context of clinically-modelled SCI. The status of these circuits after SCI is increasingly more important with the accumulation of data demonstrating the efficacy of activity-dependent task-specific training (i.e., physical therapy), and the reliance of that therapy on both appropriate sensory input and “healthy” caudal spinal cord circuitry.
Biomedical hypothesis-driven projects
1) Mechanisms of adult axonal collateral sprouting
This project investigates the molecular-level regulation of adult axonal collateral sprouting – the extension of new axonal branches from non-injured neurons. Putative regulatory factors and pathways were identified principally from analysis of the transcriptome (mRNA microarray) using a “spared dermatome” model, where non-injured sensory neurons extend their axons into adjacent denervated skin. This project has identified factors regulated specifically in sprouting, as opposed to regeneration, which represent a rational pathway from external signal to internal cytoskeletal response and transcriptional regulation. We are also determining the degree to which sprouting and regeneration differ.
2) Mechanisms and consequences of sensory neuron responses to tissue damage
This project investigates the mechanisms by which sensory neurons innervating injured/inflamed tissue are induced to express injury/regeneration-like genes. It also investigates the effects of this gene expression on the anatomical and electrophysiological properties of the affected sensory neurons. We are also identifying clinically-applicable treatments which can reduce this injury/stress to reduce the impact on the nervous system of damage to peripheral tissue.
3) Effects of spinal cord injury and post-SCI treatments on motoneuron function
This project investigates the effects of graded contusion SCI on the electrophysiological properties of hindlimb motoneurons. Secondarily, the electrophysiological parameters of motoneurons are related directly (i.e. from the same animals) to behavioral measures (step/swim kinematics, weight-support capacity) and molecular measures (levels of neurotrophins and neurotrophin receptors in relevant muscles, DRG, and spinal cord segments). Further, we determine the effects of post-SCI viral vector-mediated delivery of neurotrophic factors on these same parameters.
Projects developing model systems and tools
1) “Functional reporter” gene for use with intracellular electrophysiology
This project aims to develop “functional reporters” – genes that can report on the genetic status of single cells to electrophysiological probes independent of optical detection. For example, frequently-used reporters such as GFP are undetectable by electrodes. Further, for applications such as in vivo electrophysiology in rodents and larger animals many targets are simply too deep to employ microscopy in parallel with electrophysiology. Thus, to enhance the throughput and analytical power of “blind” single-cell electrophysiology, I am developing a reporter gene that will signal in real time in a manner detectible by intracellular electrodes. Supported by a grant from NIH.
2) Injury/stress reporter-mouse lines for use with imaging and electrophysiology
This project aims to develop at least 2 new lines of transgenic mice that will express fluorescent and optogenetic proteins in cells that are actively responding to stress (e.e., analog), or have been stressed at some specific time in the past (i.e., digital). These mice will enable the selective visualization (e.g., fluorescence microscopy), isolation (e.g., FACS, LCM), and activation (e.g., by Channelrhodopsin-2) of injured/stressed neurons (or other cells) amongst a mixed population. Supported by a multi-PI grant from NIH (co-PI Tsonwin Hai of The Ohio State University).
3) Bioinformatic analysis tools
This project is a collaboration with Dr. Eric Rouchka, Director of the Laboratory of Bioinformatics at the University of Louisville. We are building new analytical tools to meet needs that arose from a microarray project in my lab, but that will be applicable to many contexts. These tools include: 1) a system to inter-convert the many different gene identifiers using the genomic sequences as an absolute reference frame; 2) a system to analyze large-scale expression data (e.g., microarray, RNA-seq, etc.) from 2 different samples that may interact to predict/determine molecular interactions that may not be indicated by current analytical tools which assume a sample of homogeneous cells; 3) a system to assess the annotations of genes identified from large-scale expression data to make determinations/predictions about what cellular processes may be active in certain conditions; 4) a system to examine microarray and RNA-seq data for differential regulation of different regions of transcripts (i.e., to identify genes whose regulation differs based on exon splicing, UTR extensions, etc.).
4) CTM reflex as a model system
This project characterizes the organization of the cutaneus trunci muscle (CTM) reflex system and develops it as a model system for testing hypotheses, particularly those related to spinal nociception/pain, propriospinal neuron function, and plasticity in sensory and motor neurons. It is already validated as a monitor for sensory neuron collateral sprouting through skin and for efficacy of anesthetic and analgesic agents.